This invention relates to an exposure apparatus of raster scanning type using an electron beam.
Shown in FIG. 1 is a known exposure apparatus of raster scanning type using electron beams. The exposure apparatus has a electron beam generator 2 which is driven by a scanning device 4 to generate an electron beam for scanning a test piece 6 put on a table 8 in the horizontal direction or X direction. The electron beam generator 2 is connected to receive dot pattern data which have been read out from a random access memory 10 by a central processing unit 12 and which have been supplied via a direct memory access 14 and a buffer 16. The table 8 is moved by a driver 18 which responds to clock pulses from a clock pulse generator 20. The scanning device 4 responds also to these clock pulses to drive the electron beam generator 2. Each time the electron beam generator 2 has generated an electron beam required for scanning one line extending in X direction, in accordance with the dot pattern data the driver 18 moves the table 8 by a one-line space distance in the vertical direction or Y direction and the scanning device 4 sets the electron beam generator 2 to an initial state for scanning the next line.
If adjacent lines are constituted by the same dot pattern data, the dot pattern data are repeatedly used to compress the data which are to be transferred from RAM 10 to the buffer 16, thus elevating pattern-drawing speed. In case a pattern includes a slant line, however, the dot pattern data vary for every line. Thus, it is impossible to continuously draw a slant line on the test piece 6. If different patterns are drawn on adjacent test pieces or chips by exposing the chips to an electron beam, the pattern-drawing speed is inevitably reduced. Further, in order to draw various patterns, a large amount of dot pattern data is required and it is required to use RAM 10 having a large memory capacity.